Synthesis of bentonite clay-based iron nanocomposite and its use as a heterogeneous photo fenton catalyst

ABSTRACT

The present invention provides a method of synthesizing bentonite clay-based Fe nanocomposite, that may be used as a heterogeneous photo Fenton catalyst in advanced oxidation processes (AOP&#39;s) for wastewater treatment.

FIELD OF THE INVENTION

This invention relates to synthesis of a bentonite clay based Fenanocomposite and its application as a heterogeneous photo Fentoncatalyst in Advanced Oxidation Processes (AOP's) for wastewatertreatment.

BACKGROUND OF THE INVENTION

Wastewaters generated in chemical and textile industry containsignificant amounts of organic pollutants, such as azo dyes. Theycontribute significantly to water pollution, and most of them arestringently controlled by legislation. Azo dyes are very toxic toplants, animals, and human beings, and therefore must be treated beforebeing discharged.

During the past ten years, various advanced oxidation processes (AOP's)have been developed for the treatment of the wastewater containingorganic pollutants. In principle, AOP's are based on the generation ofOH radicals in water, which are highly oxidative, nonselective, able tooxidize organic compounds, particularly unsaturated organic compoundssuch as azo dyes. Among AOP's, one of the most important processes togenerate OH radicals is using the Fe²⁺/H₂O₂/UV system, where thecatalyst ferrous ions are dissolved in water. Called homogeneousphoto-Fenton system, the Fe²⁺ ions in solution function as a homogeneouscatalyst. The formation of OH radicals and regeneration of Fe²⁺ by photoreduction from Fe³⁺ can be expressed by the following equations:Fe²⁺+H₂O₂+UV→Fe³⁺+•OH+OH—  (1)Fe(OH)²⁺+UV→Fe²⁺+•OH   (2)

The homogeneous photo-Fenton process, however, has at least onesignificant disadvantage. The removal of the sludge containing Fe ionsat the end of wastewater treatment is rather costly, and requires largeamounts of chemicals and manpower. This drawback limits the use ofhomogeneous photo-Fenton reaction in industry wastewater treatment. Toovercome the disadvantage of homogeneous photo-Fenton process, someattempts have been made to develop a heterogeneous photo-Fenton orphoto-Fenton-like process by coating Fe ions, Fe oxide or Cu onto poroussolid support as the catalyst. This heterogeneous catalyst does notdissolve in water. To prepare a heterogeneous catalyst for photo-Fentonprocess, various supports have been used including organic and inorganicmaterials.

For example, Nafion film has been used as an organic support in thisprocess. It contains sulfonic groups that can effectively anchor Feions, on which Na ions can be replaced by Fe³⁺ ions through a simple ionexchange reaction. For example, J. Fernandez et al. prepared thecatalyst with Nafion perfluorinated cation transfer membrane (Dupont117, 0.007 in, Aldrich #7 467-4) containing hydrophilic sulfonate groupsimmobilized on the fluorocarbon matrix. The ion exchange with FeCl₃.6H₂Owas carried out for a few minutes after the Nafion membrane was immersedin HCl solution. After the ion exchange, the membrane was washed withwater followed by immersion in 1 M NaOH to convert Fe³⁺ to its hydratedform.

They used the catalyst for the abatement of non-biodegradable azo-dye inthe presence of UV light and H₂O₂. However, the Nafion film basedcatalyst has many disadvantages, even though the catalyst can beseparated easily from solution. First, the Nafion film catalyst showedlow photo catalytic activity due to its low specific surface area.Second, the catalyst is too expensive to be used as a heterogeneousphoto Fenton catalyst in industrial wastewater treatment. The price ofNafion film is quite high.

In addition to Nafion film, Nafion pellets containing sulfonic groupswere also employed as an organic support for the preparation ofheterogeneous photo Fenton catalyst. Puma and Yue prepared Fe-Nafionpellets through ion exchange method, and used them as a heterogeneousphoto Fenton catalyst in the oxidation of Indigo Carmine dye. Theirpreliminary result indicates that the Fe-Nafion pellets are effective inreducing the concentration of the dyes in solution. However, theFe-Nafion pellet catalyst also shows low photo catalytic activity andhigh cost.

Apart from Nafion film and Nafion pellets, another support used for thepreparation of heterogeneous photo Fenton catalyst is zeolite Y.Bossmann et al. prepared Fe (III) doped zeolite Y as the heterogeneousphoto Fenton catalyst in the oxidation of PVA. They found that contraryto the homogeneous reaction mechanism, the degradation of PVA using thesystem zeolite Y/Fe(III)/H₂O₂ generates low molecular weight reactionproducts because DOC-removal remains at a high level after reacting 120minutes. In addition, they confirmed that Fe(III) does not formcomplexes with PVA and its oxidation products. Most likely, the Fe(III)remains bound inside the zeolite Y framework. Their results reveal thatthe catalyst has a poor photo catalytic activity.

Further, Hu et al. prepared copper/MCM-41 as catalyst forphotochemically enhanced oxidation of phenol by hydrogen peroxide.Because MCM41 is an expensive support, the catalyst also hasdisadvantages similar to Nafion based catalyst. Apart from this, thecatalyst exhibited a low photo catalytic activity in the oxidation ofphenol in the presence of UV light and H₂O₂. In other words, similar toNafion based catalyst mentioned above, introducing a cheap catalyst onan expensive support is not a good choice.

U.S. Pat. No. 5,755,977 (Gurol) discusses a continuous catalyticoxidation process. In this process, particulate mineral oxide selectedfrom iron oxide, manganese oxide, mixtures of iron oxide and manganeseoxide, and mixtures containing these mineral oxides were used ascatalysts. The process does not appear to involve UVC light.

U.S. Pat. No. 6,663,781 (Huling) relates to contaminant adsorption andoxidation via the Fenton reaction. In the process, iron was attached togranulated activated carbon. The obtained iron.GAC was used as anadsorbent and a catalyst via the Fenton reaction for contaminantadsorption and oxidation.

Based on the discussions above, there is a need for a high efficiency,low cost heterogeneous catalyst for photo-Fenton reaction. Layered clayssuch as laponite and bentonite have been used as catalyst supports dueto their unique properties and structures, their abundance, andrelatively low cost. For example, Wang et al. developed clay-basednickel catalysts for methane reforming. Zhu et al. pointed out that somekinds of layered clay such as laponite has very small platelets, 20-30nm in diameter, while Fe₂O₃ can be intercalated as pillars. Thepillaring technique has been described by Burch, R. Ed. Pillared Clays,Catalysis Today, Elsevier: New York, 1998, and Mitchell, I V., Ed.Pillared Layered Structures, Current Trends and Applications, ElsevierApplied Science, London, 1990. In addition, both Feng et al. and He etal. showed that nano-sized Fe₂O₃ exhibited photo catalytic activity as aheterogeneous photo Fenton catalyst in the presence of H₂O₂ and UVlight.

U.S. Pat. No. 5,202,295 (McCauley) discloses the intercalated clayhaving large interlayer spacing.

U.S. Pat. No. 4,980,047 (McCauley) describes stable intercalated claysand preparation method. However, their intercalated clays are mainlyused as oil cracking catalysts.

The biggest advantages of the bentonite clay based Fe nanocomposite as aheterogeneous photo Fenton catalyst for wastewater treatment can besummarized as follows: (1) high photo catalytic activity; (2) long-termstability; and (3) low cost.

OBJECTS OF THE INVENTION

It is, therefore, the primary object of this invention to develop abentonite clay based Fe nanocomposite using so-called pillaringtechnique.

It is a further object of this invention to employ this Fe nanocompositeas a heterogeneous photo Fenton catalyst in Advanced Oxidation Processesfor wastewater treatment at optimal solution pH.

It is a further object of this invention to employ this Fe nanocompositeas a heterogeneous photo Fenton catalyst in Advanced Oxidation Processesfor wastewater treatment at initial solution pHs.

SUMMARY OF THE INVENTION

The invention provides a method for synthesizing a bentonite clay-basedFe nanocomposite (Fe—B), using a pillaring technique, comprising thesteps of: (a) forming an aqueous bentonite suspension; (b) forming anFe³⁺ pillaring solution by adding powder NaCO₃ to an Fe(NO₃)₃ aqueoussolution; (c) adding the Fe³⁺ pillaring solution obtained in step (b) tothe aqueous bentonite suspension obtained in step (a) with vigorousstirring to form bentonite Fe³⁺ pillaring solution mixture; (d) agingthe mixture at room temperature or 100° C. for 48 hours; (e) separatingby centrifugation and washing the mixture to obtain a catalyst precursorprecipitate; and (f) calcining the catalyst precursor to formintercalated bentonite iron oxide catalyst nanoparticles.

The invention also provides a reactor for treatment of wastewater,comprising: a stainless steel vessel having Fe—B nanoparticles inaccordance with claim 1 sprayed to form a layer thereof on an inner wallsurface; a UV light source to irradiate wastewater in the reactor; ahydrogen peroxide source for adding hydrogen peroxide to wastewater inthe reactor; means for introducing wastewater in the reactor fortreatment; and means for removing wastewater from the reactor aftertreatment.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, advantages and features of the present invention willbecome apparent upon consideration of the following detailed disclosure,taken in conjunction with the drawings, in which some embodiments ofpresent invention will now be described by way of example and withreference to accompanying drawings, in which:

FIG. 1 is a schematic diagram illustrating the synthesis of a bentoniteclay based nanocomposite by the pillaring technique;

FIG. 2 is an x-ray diffraction pattern of a Fe—B nanocomposite;

FIG. 3 is a schematic diagram of a batch photo reactor wherein the Fe—Bnanocomposite of the present invention is used as a dispersedheterogeneous photo Fenton catalyst;

FIG. 4 plots discoloration of 0.2 mM Orange II in a batch reactor underdifferent conditions;

FIG. 5 plots Fe concentration in solution under different conditions;

FIG. 6 plots mineralization of 0.2 mM Orange II in a batch reactor underdifferent conditions;

FIG. 7 plots discoloration of 0.2 mM Orange II in a batch reactor underdifferent initial solution pHs;

FIG. 8 plots mineralization of 0.2 mM Orange II in a batch reactor underdifferent initial solution pHs;

FIG. 9 is a schematic diagram of a batch photo reactor when the Fe—Bnanocomposite film is used as a heterogeneous photo Fenton catalyst;

FIG. 10 plots discoloration of 0.2 mM Orange II in a batch reactor underdifferent conditions;

FIG. 11 plots mineralization of 0.2 mM Orange II in a batch reactorunder different conditions;

FIG. 12 plots multi-run experiments; and

FIG. 13 is a schematic diagram of a batch falling film photo reactorwhen the Fe—B nanocomposite film is used as a heterogeneous film photoFenton catalyst.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a method for synthesizing bentonite clay-based Fenanocomposite (Fe—B), using a pillaring technique, comprising the stepsof: (a) forming an aqueous bentonite suspension; (b) forming an Fe³⁺pillaring solution by adding powder NaCO₃ to an Fe(NO₃)₃ aqueoussolution; (c) adding the Fe³⁺ pillaring solution obtained in step (b) tothe aqueous bentonite suspension obtained in step (a) with vigorousstirring to form bentonite Fe³⁺ pillaring solution mixture; (d) agingthe mixture at room temperature or 100° C. for 48 hours; (e) separatingby centrifugation and washing the mixture to obtain a catalyst precursorprecipitate; and (f) calcining the catalyst precursor to formintercalated bentonite iron oxide catalyst nanoparticles.

The invention further provides a process for treating wastewatercomprising: providing a reactor vessel containing Fe—B nanocompositedispersed nanoparticles heterogeneous photo Fenton catalyst; introducinguntreated wastewater into the reactor vessel; and exposing thewastewater to H₂O₂ in the presence of UV light to oxidize contaminantsin the wastewater. Preferably, the process is carried out at a pH ofbetween about 2.8 through 3.2, and the initial solution pH ranges fromabout 2.8 through 7.0.

The invention also provides a process for treating wastewater in areactor vessel, wherein the reactor vessel is stainless steel and theFe—B nanoparticles are spray coated on the surface thereof by a hotspray method to form a layer thereon. Preferably, the stainless steelsurface is sand blasted prior to spray coating. The Fe—B nanoparticlesare coated on the inner wall surface of a reactor, such as a batch photoreactor, and are used as a photo Fenton catalyst in the presence of UVlight and H₂O₂ for wastewater treatment at an initial solution pH ofbetween about 2.8 to 7.0.

In another embodiment, the Fe—B nanocomposite film is coated on theinner wall surface of a cylindrical falling film photo reactor, and isused as a photo Fenton catalyst in the presence of UVC light and H₂O₂for the wastewater treatment at an initial solution pH of between about2.8 and about 7.0.

The invention additionally provides a reactor for treatment ofwastewater, comprising: a stainless steel vessel having Fe—Bnanoparticles sprayed on the inside surface thereof to form a layerthereof on an inner surface; a UV light source to irradiate wastewaterin the reactor; a hydrogen peroxide source for adding hydrogen peroxideto wastewater in the reactor; means for introducing wastewater in thereactor for treatment; and means for removing wastewater from thereactor after treatment.

In a further embodiment, the stainless steel vessel is an elongatedcolumn with a UV light source disposed therein, and the wastewater canbe continuously processed in a reactor loop. Preferably, the UV lightsource is a UVC light source.

The invention also provides a process for the synthesis of a bentoniteclay based Fe nanocomposite (Fe—B), and its use as a heterogeneous photoFenton catalyst in AOP's for wastewater treatment are provided for thefirst time.

The synthesis of Fe—B nanocomposite was performed using the so-calledpillaring technique. In this synthesis, when bentonite clay wasdispersed in water, it swelled significantly because of hydration of theinterlamellae cations which act as counterions to balance the negativecharges of the bentonite clay layers. Then, the inorganic polycations,the so-called pillar precursors could be intercalated the interlayergallery by cation exchange. During subsequent calcinations at hightemperature, the intercalated Fe ions are converted iron oxide pillarsthat prop the clay layer apart. Because the interlayer distance is innano-scale, the size of iron oxide is also in nano-scale. Consequently,the Fe—B nanocomposite is synthesized.

It was discovered that as a heterogeneous photo Fenton catalyst, theFe—B nanocomposite exhibited a high photo catalytic activity andlong-term stability in the discoloration and mineralization of azo dyeOrange II in the presence of UVC (254 nm) and H₂O₂. In addition, it hasa low cost.

The Fe—B nanocomposite can be used a dispersed heterogeneous catalyst ina batch photo reactor for the wastewater treatment or as a film catalystin a batch or continuous falling film photo reactor for the wastewatertreatment.

The present invention represents the synthesis of bentonite clay basedFe nanocomposite (Fe—B) for the first time. The theoretical principlefor the synthesis of the Fe—B nanocomposite is illustrated in FIG. 1,and includes several steps set forth as follows: (a) bentonite clayswells when dispersed in water; (b) ion exchange between the cations onthe clay and Fe³⁺ ions in pillaring solution; and (c) calcinationconverts Fe³⁺ ions between the layers of bentonite into Fe₂O₃ pillars.

The nano-sized Fe₂O₃ particles or composites containing nano-sized Fe₂O₃can work as a heterogeneous photo Fenton catalyst in the presence of UVlight and H₂O₂. Possible mechanisms for generating •OH radicals areexpressed as follows:

Feng et al. proposed a mechanism for a laponite clay based Fenanocomposite (Fe-Lap-RD) functioning as a heterogeneous photo Fentoncatalyst in the discoloration and mineralization of Reactive Red HE-3Bin the presence of UVC light and H₂O₂. In this mechanism:Fe³⁺ on the surface of Fe-Lap-RD+hν→Fe²⁺ on the surface of Fe-Lap-RD  (3)Fe²⁺ on the surface of Fe-Lap-RD+H₂O₂→Fe³⁺ on the surface ofFe-Lap-RD+•OH+OH⁻  (4)Fe-lap-RD-HE-3B+•OH→Reaction intermediates→CO₂+H₂O   (5)

The reactions are initiated by the photo-reduction of Fe³⁺ on thesurface of Fe-Lap-RD to Fe²⁺ under irradiation of UV light. Then, theFe²⁺ formed accelerates the decomposition of H₂O₂ adsorbed on thesurface of Fe-Lap-RD, generating highly oxidative OH radicals while theFe²⁺ is oxidized by H₂O₂ into Fe³⁺. Furthermore, the OH radicals attackHE-3B adsorbed on the surface of the Fe-Lap-RD, giving rise to reactionintermediates such as adjacent ring structures. Finally, the reactionintermediates are mineralized into CO₂, H₂O, and small amount ofinorganic acid.

He et al. proposed another mechanism in the heterogeneous photo Fentondegradation of an Azo dye MY 10 as described as below:≡Fe^(III)OH+H₂O₂→≡Fe^(III)OOH+H₂O≡Fe^(III)OOH+hν→≡Fe^(IV)=O+•OH≡Fe^(IV)=O+H₂O→≡Fe^(III)OH+•OHMY10+•OH→degraded or mineralized products

Using the Fe—B as a dispersed catalyst in water increases efficiencybecause the catalyst has a large BET surface area. The disadvantage ofFe—B as a dispersed catalyst is that after reaction, a filtrationprocess is needed.

An important improvement for the Fe—B catalyst is to coat the Fe—Bcatalyst on stainless steel surface as a catalyst film or layer using aFe—B catalyst film or layer avoids the filtration or separation step.This process can pre-treat wastewaters before they undergo biologicaltreatment.

The following examples are presented to illustrate the presentinvention, but should not be considered as a limitation of the scopethereof.

EXAMPLE 1 Synthesis of Fe—Bentonite Nanocomposite

The Fe—B nanocomposite was prepared through the following steps:

-   -   (a) An aqueous dispersion of bentonite clay was prepared by        adding 10 g bentonite clay to 500 ml H₂O under vigorous stirring        for 3 hours at room temperature. The bentonite clay was obtained        from Integrated Mineral Technology Ltd, Australia.    -   (b) Sodium carbonate Na₂CO₃ was added slowly as a powder into a        vigorously stirred 0.2 M solution of iron nitrate for 3 hours        such that a molar ratio of 1:1 for [Na⁺]/[Fe³⁺] was established.        Na₂CO₃ and Fe₃(NO₃)₃.9H₂O were purchased from Aldrich.    -   (c) 500 ml solution obtained from the step (b) was then added        drop-wise into the dispersion of bentonite clay prepared in the        first step, under vigorous stirring.    -   (d) The suspension was stirred for 3 hours followed by aging at        100° C. in an autoclave for 48 hours. The precipitate was        recovered from the mixture by centrifuging, and then washed with        deionized water to remove all Na ions. The precipitate was dried        in air at 120° C. overnight.

(f) The dried solid was calcined at 350° C. for 24 hours and theFe—Bentonite nanocomposite Fe—B was obtained. The X-ray diffractivepattern in FIG. 2 indicates that the Fe—B nanocomposite mainly consistsof Fe₂O₃ (hematite) and SiO₂ (quartz) crystallites. The BET surfacespecific area was determined to be 280 m²/g. The Fe concentration withrespect to the total weight is 31.8 wt %. The Fe concentration in theFe—B nanocomposite was also measured by ICP. The Fe concentration is33.8 wt %, which agrees well with the result obtained by x-raydiffraction. Table 1 shows the bulk chemical compositions of the Fe—Bnanocomposite: TABLE 1 Bulk Chemical Compositions of Fe—B NanocompositeDetermined by XRF Element concentration (wt %) O 45.1511 Na 0.1176 Mg0.7271 Al 4.4895 Si 17.2437 K 0.0717 Ca 0.0252 Ti 0.0796 Mn 0.2780 Fe31.8165

Table 2 lists surface atomic compositions and binding energy of the Fe—Bnanocomposite determined by XPS: TABLE 2 Surface Atomic Compositions andBinding Energy (BE) of Fe—B Nanocomposite Determined by XPS AtomicBinding Element concentration (at %) energy (eV) C1s 6.05 284.8 O1s60.23 531.6 Mg1s 1.08 1303.9 AI2p 4.86 74.2 Si2p 15.53 102.1 Ca2p3 0.01351.8 Fe2p 12.25 711.8

EXAMPLE 2 Fe—B Nanocomposite As A Heterogeneous Photo Fenton Catalyst Inthe Discoloration And Mineralization of Azo Dye Orange II At An OptimalInitial Solution PH of 3.0

The model pollutant for the evaluation of Fe—B catalyst is an azo-dye,Orange II, a non-biodegradable dye widely used in textile industry.Thus, it is a suitable model pollutant. The Orange II was available fromAcros Organics, USA. The photo-Fenton discoloration and minerlization ofOrange II was performed in a photo reactor 10, as shown in FIG. 3. It iscylindrical with a UVC lamp 12 (Philips 8 W 254 nm) inserted in aquality table 14 the center.

A stirring bar 16 driven by an electromagnetic stirrer 18 vigorouslystirs the reaction solution 20. A water jacket 22 through which waterenters 24 and exits 26 cools (or possible warms) the reaction solution20 as needed. The total volume of Orange II solution was 0.5 liter andthe initial Orange II concentration used was fixed at 0.2 mM exceptotherwise specified. The reaction solution pH was adjusted to 3.0±0.1,which is the optimal value for the (photo) Fenton reaction. The reactiontemperature was controlled to be 30° C. by a water bath except otherwisespecified. In order to ensure a good dispersion of the Fe—B catalyst inthe Orange II solution, an electromagnetic stirrer was used. Thestarting point of the reaction was treated as the time when the UV lightwas turned on and 30% by weight H₂O₂ (Aldrich) was added to the OrangeII solution.

FIG. 4 shows the relative Orange II concentration versus time underdifferent conditions. The Orange II concentration was determined by anUV-VIS spectrometer (Shimadzu UV MINI 1240 UV-VIS spectrophotometer).Without Fe—B catalyst and H₂O₂, with only 1×8 W UVC (curve a), there islittle discoloration of Orange II, because the Orange II itself canresist UVC light. Without UVC light (dark) and H₂O₂, with only 1.0 gFe—B/L (curve b), the decrease in the Orange II concentration is veryfast in the first 15 minutes and then reaches a steady state of 30%removal. The fast decrease in the first 15 minutes is due to theadsorption of Orange II on the surface of Fe—B catalyst. The adsorptioncapacity of Fe—B catalyst is estimated to be around 20 mg Orange II/gFe—B catalyst. Without Fe—B catalyst, but with 10 mM H₂O₂ and 1×8 W UVC(curve c), the discoloration of Orange II is quite significant, owing tothe oxidation of Orange II by OH radicals from the direct photolysis ofH₂O₂ in the presence of 1×8 W UVC. Without UVC light (dark), but with1.0 g Fe—B/L and H₂O₂ (curve d), the discoloration of Orange II iscontinuous.

Apparently, there are two processes contributing to the discoloration ofOrange II observed. One is the adsorption of Orange II on the surface ofFe—B, which causes the discoloration of Orange II in the first 15minutes. Also, the oxidation of Orange II by OH radicals coming fromFenton reaction causes the discoloration of Orange II after 15 minutes.However, the discoloration of Orange II using a Fenton reaction insteadof photo-Fenton reaction is not effective. With 1×8 W UVC, 1.0 g Fe—B/L,and 10 mM H₂O₂ (curve e), the discoloration of Orange II appears to workbest. Complete discoloration of Orange II can be achieved in less than60 minutes. However, we are unsure whether faster discoloration ofOrange II is due to the oxidation of Orange II by the OH radicals comingfrom the heterogeneous photo-Fenton reaction or from homogeneousphoto-Fenton reaction owing to the Fe ions leaching from the Fe—Bcatalyst.

To address this issue, the Fe ion concentrations versus time underdifferent conditions in solution were measured. With and withoutcatalyst, the Fe ion concentration in reaction solution as a function oftime was measured by Inductively Coupled Plasma (ICP) (Perkin ElmerModel: 3000 XL), and the results are presented in FIG. 5. Clearly, thereaction conditions can significantly influence Fe ion concentration insolution. Without any Fe—B catalyst (curves a and c), the Fe ionconcentrations are near zero, as expected—because there is no Feleaching. Without H₂O₂ and UVC light (dark), only with 1.0 g Fe—B/L(curve b), the Fe leaching is less than 1 mg/L. After 120 minutesreaction, indicating that Fe leaching from the Fe—B catalyst is notsignificant. Similar results were observed under conditions of 1.0 gFe—B/L, 10 mM H₂O₂, and in the dark (see curve d). With 1×8 W UVC, 1.0 gFe—B/L, and 10 mM H₂O₂ (curve e), the Fe ion concentration in solutionincreases initially from 0 to a peak value (about 2.2 mg/L) at about 30minutes followed by a continuous decrease to a steady value (around 1.0mg/L). The mechanism for this phenomenon is still unknown. Based on theresults above, it can be deduced that the fast discoloration of 0.2 mMOrange II comes from three processes. The first is the adsorption ofOrange II on the surface of Fe—B catalyst; the second is the oxidationof Orange II by heterogeneous photo-Fenton reaction; and the last is theoxidation of Orange II by homogeneous photo-Fenton reaction. However, itshould be noted that near 90% removal of Orange II occurs in the first10 minutes, and at that time Fe ion concentration is less than 1.0 mg/L.Therefore, the heterogeneous photo Fenton reaction appears to be mainlyresponsible for the fast discoloration of Orange II.

The TOC of 0.2 mM Orange II as a function of time under differentconditions were measured and the results are illustrated in FIG. 6.Without H₂O₂ and Fe—B catalyst, only with 1×8 W UVC (curve a), the TOCof Orange II does not decrease at all indicating that direct photolysisof Orange II cannot cause any mineralization of Orange II. Without UVClight (dark) and 10 mM H₂O₂, but with 1.0 g Fe—B catalyst/L (curve b),the TOC decreases in the first 15 minutes, then, reaches a steady statevalue. As discussed earlier, this phenomenon is totally due to theadsorption of Orange II in solution on the surface of Fe—B catalyst.Without Fe—B catalyst, but with 10 mM H₂O₂, and with 1×8 W UVC (curvec), the TOC decreases rapidly in the first 10 minutes, then slowlycontinues to decrease. The limited slow mineralization is caused by theoxidation of Orange II due to the OH radicals coming from the directphotolysis of H₂O₂. However, it should be stressed that after 120minutes, only around 30% of TOC was removed while more than 95%discoloration was achieved. This result implies that the OH radicalsfrom the direct photolysis of H₂O₂ can only oxidize the Orange II intolonger-lived colorless intermediates but cannot completely mineralizeOrange II into H₂O and CO₂. Without UVC light (dark), but with 10 mMH₂O₂, and 1.0 g Fe—B/L (curve d), the TOC decreases in the first 10minutes due to both adsorption of Orange II on the surface of Fe—Bcatalyst and oxidation of Orange II by Fenton reaction. From 10 to 15minutes, the slight increase in TOC appears to stem from the absorptionof Orange II on the surface of the Fe—B catalyst. The complexre-dissolves into the water; the original Orange II is not completelymineralized into H₂O and CO₂, but into some colorless intermediates. Thefurther decrease in TOC is attributed to the Fenton reaction. As can beseen from curve d, after 120 minutes, only 50% TOC was removed, implyingthat Fenton instead of photo-Fenton reaction is not an effectivetechnique for quick complete mineralization of Orange II. With 10 mMH₂O₂, 1.0 g Fe—B/L, and 1×8 W UVC (curve e), the TOC shows a quickdecrease in the first 10 minutes, then a slightly increase followed by acontinuous decrease to 100% removal. The decrease in the first 10minutes is caused by both adsorption of Orange II on the surface of Fe—Bcatalyst and the oxidation of Orange II by OH radicals fromheterogeneous photo-Fenton reaction. After that, the slight increase inTOC is again attributed to the fact that the Orange II adsorbed on thesurface of Fe—B catalyst redissolve into solution due to the fastdecrease in Orange II concentration as shown in FIG. 4 (curve e). Thefollowed continuous decrease in TOC arises from oxidation of Orange IIby OH radicals coming from the heterogeneous photo-Fenton reaction.After 120 minutes, the TOC almost reaches to zero. The result indicatesthat the presence of Fe—B catalyst can effectively mineralize Orange IIinto H₂O and CO₂.

EXAMPLE 3 Fe—B Nanocomposite As A Heterogeneous Photo Fenton Catalyst Inthe Discoloration And Mineralization of Azo Dye Orange II At DifferentInitial Solution PHs

The effect of initial solution pH on the discoloration of 0.2 mM OrangeII was first studied in the discoloration of 0.2 mM Orange II in thepresence of 10 mM H₂O₂, 1.0 g/L Fe—B, and 1×8 W UVC light, and theresult is shown in FIG. 7. Apparently, the initial solution pH cansignificantly influence the discoloration kinetics of 0.2 mM Orange II,indicating that initial solution pH can impose a great impact on thecatalytic activity of Fe—B nanocomposite. The Fe—B nanocompositeexhibited the best catalytic activity at pH=3.00 while it showed adecreased catalytic activity when the initial solution pH departs from apH of 3.00. However, it should be stressed that even at a pH of 6.60,which is very close to neutral, complete discoloration still could beachieved in less than 90 minutes, implying that the Fe—B catalyst stillexhibited good photo catalytic activity at a high pH value.Significantly, the solution pH changes after 120 minutes reaction, andthe extent of this change strongly depends on the initial solution pH.When the initial solution pHs are 2.10 and 3.00, the solution pH's after120 minutes reaction increase slightly. When the initial solution pH is4.06, the solution pH after 120 minutes slightly decreases. However,when the initial pHs are 5.16 and 6.60, the solution pHs after 120minutes reaction decreases significantly.

To explain the change in solution pH, the complete mineralization ofOrange II is described by the equation below:C₁₆H₁₁N₂NaO₄S+42H₂O₂→16CO₂+46H₂O+2HNO₃+NaHSO₄   (3)

In addition to the discoloration, we are more interested in themineralization of 0.2 mM Orange II in the presence of 10 mM H₂O₂, 1.0g/L Fe—B, because even though complete discoloration of 0.2 mM Orange IIcould be achieved at less than 90 minutes as shown above, reactionintermediates may form, which might be more toxic than Orange II itself.Therefore, from the point view of a industrial wastewater treatment,complete mineralization or 100% TOC removal is more desirable than 100%discoloration, because only when 100% TOC removal is achieved, allorganic intermediates in solution are mineralized into CO₂ and H₂O. FIG.8 displays the effect of initial solution pH on the mineralization of0.2 mM Orange II in the presence of 10 mM H₂O₂, 1.0 g/L Fe—B, and 1×8 WUVC light.

As can be seen from the figure, initial solution pH can markedlyinfluence the mineralization of 0.2 mM Orange II. At initial solutionpH=3.00, 100% TOC removal of 0.2 mM Orange II is achieved after 120minutes reaction, indicating that the Fe—B nanocomposite exhibited thehighest catalytic activity at this initial solution pH. However, asinitial solution pH increases from 3.0 to 6.60, the mineralizationkinetics become slower, indicating that the Fe—B nanocomposite showed adecreased photo catalytic activity. On the other hand, as the initialsolution pH decreases from 3.00 to 2.10, the mineralization kinetics of0.2 mM Orange II also becomes slow, implying that the Fe—B nanocompositedisplays a decreased catalytic activity at pH=2.10. Notably, even whenwe started our reaction at a initial pH=4.06 to 6.60, the TOC removal of0.2 mM Orange II still can reach 60 to 75%, indicating that the Fe—Bnanocomposite exhibited reasonably good activity when initial solutionpH is near neutral pH.

EXAMPLE 4 Fe—B Nanocomposite Film Coated On the Inner Wall Surface of ABatch Photo Reactor As A Heterogeneous Photo Fenton Catalyst In theDiscoloration And Mineralization of Azo Dye Orange II

FIG. 9 shows a batch photo reactor 40, in which the discoloration of a0.2 mM Orange II reaction solution 42 under different conditions wasperformed by using a Fe—B film catalyst coated on the inner wall surface44 of the reactor 40 as a photo Fenton catalyst, and the results areshown in FIG. 10. Apparently, the discoloration kinetics of 0.2 mMOrange II are significantly influenced by experimental conditions.Without any H₂O₂ or catalyst, but with only 1×8 W UVC 46 inside a quartztube 48 (curve a), color removal is less than 5% after 120 minutes, anegligible amount. This is so because Orange II itself can resist UVClight, and direct photolysis of Orange II is very limited. Without anycatalyst but with 10 mM H₂O₂ and 1×8 W UVC, the color removal approachedto 95% after 120 minutes, implying that the discoloration of 0.2 mMOrange II is significant. Here, Orange II was oxidized by the •OHradicals coming from direct photolysis of H₂O₂ in the presence of 8 WUVC as expressed by the following equation:H₂O₂+UVC light→2•OH   (4)

Without any UV light (dark), but with 10 mM H₂O₂ and the catalyst (curvec), the color removal of 0.2 mM Orange II was less than 20% after 120minutes reaction, indicating that the discoloration of 0.2 mM Orange IIis very slow. This is so because without any UV light, heterogeneousFenton reaction itself is very slow, resulting in very limited OHradicals. Accordingly, a very slow discoloration of 0.2 mM Orange IIoccurred. With 1×8 W UVA, 10 mM H₂O₂, and the catalyst (curve d), thecolor removal of 0.2 mM Orange II was only about 80% after 120 minutesreaction, illustrating that the Fe—B film catalyst does not exhibit agood photo catalytic activity in the discoloration of 0.2 mM Orange IIin the presence of 1×8 W UVA light and 10 mM H₂O₂. In another words, UVAdoes not appear to be suitable UV light source for the Fe—B filmcatalyst. With 1×8 W UVC, 10 mM H₂O₂, and the catalyst (curve e), 100%color removal of 0.2 mM Orange II can be achieved in less than 90minutes, indicating that the Fe—B catalyst film shows a good photocatalytic activity in the discoloration of orange 11 in the presence of1×8 W UVC light and 10 mM H₂O₂. This is so because the Fe—B filmcatalyst can act as a heterogeneous photo Fenton catalyst underirradiation of 1×8 W UVC, generating more •OH radicals that can attackOrange II. As a result, fast discoloration kinetics of 0.2 mM Orange IIwas observed. In this series of experiments, the reaction solution 42was stirred vigorously using a magnetic stirrer 50 with a magneticstirring bar 52 to maximize exposure to the Fe—B catalyst film or layer44.

FIG. 11 depicts the TOC of 0.2 mM Orange II as a function of time underdifferent conditions. As expected, the mineralization kinetics issignificantly influenced by the experimental conditions. With only 1×8 WUVC, or the Fe—B film catalyst+10 mM H₂O₂+dark, or the Fe—B filmcatalyst+10 mM H₂O₂+8 W UVA, no significant mineralization of 0.2 mMOrange 11 was observed, implying that these experimental conditions arenot effective at all in the mineralization of 0.2 mM Orange II.

With 10 mM H₂O₂+1×8 W UVC but no catalyst, the TOC removal of 0.2 mMOrange II was only about 25%, suggesting that mineralization of 0.2 mMOrange II caused by the attack of •OH radicals coming from directphotolysis of irradiation of 1×8 W UVC is not effective.

There are two possible reasons for this observation. The first is thatdirect photolysis of H₂O₂ generates a limited number of •OH radicals.The second is that the •OH radicals formed in solution are short-lived,and many of them decay before meeting Orange II molecules or reactionintermediates. Both reasons are responsible for the lower extent ofmineralization of 0.2 mM Orange II. However, in the case of the Fe—Bfilm catalyst +10 mM H₂O₂+8W UVC, more than 50-60% TOC removal of 0.2 mMOrange II was achieved after 120 minutes reaction, illustrating that theFe—B film catalyst as a photo Fenton catalyst also exhibited reasonablygood photo catalytic activity in the mineralization of 0.2 mM Orange IIin the presence of 10 mM H₂O₂ and 1×8 W UVC. Because the •OH radicalsformed on the surface of the Fe—B film catalyst can effectively attackthe Orange II molecules or intermediates adsorbed on the surface of theFe—B film catalyst, rapid mineralization of 0.2 mM Orange II occurs.

Another important property of a heterogeneous photo catalyst is itslong-term stability. In order to test the long-term stability of theFe—B film catalyst in the degradation of 0.2 mM Orange II in thepresence of H₂O₂ and 1×8 W UVC, a repetitive reaction (up to the 4^(th)run) was performed. FIG. 12 shows the mineralization kinetics of 0.2 mMOrange II in the presence of H₂O₂ and 1×8 W UVC through repetitively runexperiments. Compared with the first run, no significant deactivation ofthe Fe—B film catalyst was observed, suggesting that the Fe—B filmcatalyst could have long-term stability.

EXAMPLE 5 Fe—B Nanocomposite Film Coated On the Inner Wall Surface of AFalling Film Photo Reactor As A Heterogeneous Photo Fenton Catalyst Inthe Discoloration And Mineralization of Azo Dye Orange II

FIG. 13 shows the schematic diagram of a falling film photo reactorsystem 100, in which the Fe—B nanocomposite was coated as a layer orfilm on the inner wall surface as a heterogeneous photo Fenton catalystfor the oxidation of organic pollutants in the presence of UVC light andH₂O₂. The reactor system 100 includes a mix tank 102 for holdingpollutant or contaminant containing solution 104, stirred by a mixer106. Solution 104 is remixed from the mix tank 102 and pumped by pump106 through valve 108, and flow meter 110 (if desired) to the liquiddistributor 112. It collects adjacent the top of column 114 (preferablyof stainless steel) which forms an elongated column 116 having the Fe—B118 coating thereon. A UV lamp 120 is disposed centrally in a lampsleeve 122 to irradiate the solution as it passes through the column 116in contact with the Fe—B coating. Thus, the system treats contaminatedsolution with UV light 118 while it contacts the Fe—B catalyst, to breakdown the contaminants or pollutants (such as Azo dyes) containedtherein. The initial amount of contaminants or pollutants can bemeasured, and subsequent measurements can be made to determine whetherthe contaminants have been decomposed to a desired degree. If so, thesolution can be discharged, whereas it can otherwise be continuallyprocessed until it reaches the desired endpoint. Using electronicsensors, and a computer (not shown), it can be automatically controlled.

The references and patents listed below and throughout this applicationare incorporated by reference herein.

REFERENCES CITED

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Burch, R. ed., “Pillared Clays, Catalysis Today,” Elsevier: New York,1998.

Feng, J. et al., “Degradation of Azo-dye Orange II by Photo-AssistedFenton Reaction Using a Novel Composite of Iron Oxide and SilicateNanoparticles as a Catalyst,” Ind. Eng. Chem. Res., 2003, 42 (10),2058-2066.

Fernandez, J. et al., “Efficient Photo-Assisted Fenton CatalysisMediated by Fe Ions on Nafion Membranes Active in the Abatement ofNon-Biodegradable Azo-Dye,” Chem. Commun., 1998, 1493-1494

Fernandez, J. et al., “Photoassisted Fenton Degradation ofNonbiodegradable Azo Dye (Orange II) in Fe-free Solutions Mediated byCation Transfer Membranes,” Langmuir, 1999, 15 (1), 185-192.

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1. A method for synthesizing bentonite clay-based Fe nanocomposite(Fe—B), using a pillaring technique, comprising the steps of: (a)forming an aqueous bentonite suspension; (b) forming an Fe³⁺ pillaringsolution by adding NaCO₃ to an Fe(NO₃)₃ aqueous solution; (c) adding theFe³⁺ pillaring solution obtained in step (b) to the aqueous bentonitesuspension obtained in step (a) with stirring to form bentonite Fe³⁺pillaring solution mixture; (d) aging the mixture at room temperature or100° C. for 48 hours; (e) separating by centrifugation and washing themixture to obtain a catalyst precursor precipitate; and (f) calciningthe catalyst precursor to form intercalated bentonite iron oxidecatalyst nanoparticles.
 2. A process for treating wastewater comprising:providing a reactor vessel containing Fe—B nanocomposite dispersednanoparticles heterogeneous photo Fenton catalyst in accordance withclaim 1; introducing untreated wastewater into the reactor vessel; andexposing the wastewater to H₂O₂ in the presence of UV light to oxidizecontaminants in the wastewater.
 3. A process according to claim 2,wherein the process is carried out at a pH of between about 2.8 through3.2.
 4. A process in accordance with claim 2, where the initial solutionpH ranges from 2.8 through
 5. A process according to claim 2, whereinthe initial solution pH ranges from about 3.2 to 7.0.
 6. A processaccording to claim 1, wherein the reactor vessel is stainless steel andthe Fe—B nanoparticles are spray coated on the surface thereof by a hotspray method to form a layer thereon.
 7. A process according to claim 6,wherein the stainless steel surface is sand blasted prior to spraycoating.
 8. A process according to the claim 6, wherein the Fe—Bnanoparticles are coated on the inner wall surface of a batch photoreactor, and are used as a photo Fenton catalyst in the presence of UVlight and H₂O₂ for wastewater treatment at an initial solution pH ofbetween about 2.8 to 7.0.
 9. A process according to claim 6, wherein theFe—B nanocomposite film is coated on the inner wall surface of acylindrical falling film photo reactor, and is used as a photo Fentoncatalyst in the presence of UVC light and H₂O₂ for the wastewatertreatment at an initial solution pH of between about 2.8 and about 7.0.10. A reactor for treatment of wastewater, comprising: a stainless steelvessel having Fe—B nanoparticles in accordance with claim 1 sprayed toform a layer thereof on an inner surface; a UV light source to irradiatewastewater in the reactor; a hydrogen peroxide source for addinghydrogen peroxide to wastewater in the reactor; means for introducingwastewater in the reactor for treatment; and means for removingwastewater from the reactor after treatment.
 11. A reactor in accordancewith claim 10, wherein the stainless steel vessel is an elongated columnwith a UV light source disposed therein.
 12. A reactor in accordancewith claim 10, wherein the UV light source is a UVC light source.
 13. Areactor in accordance with claim 11, wherein the UV light source is aUVC light source.